Riluzole (6-(trifluoromethoxy)benzothiazol-2-amine) is a compound of formula

Riluzole, a drug used to treat amyotrophic lateral sclerosis (ALS, sometimes called Lou Gehrig's disease, Maladie de Charcot or motor neurone disease), is usually administered in an oral form at the dose of 50 mg every 12 hours and it delays the onset of ventilator-dependence or tracheostomy in selected patients.
ALS is a progressive, fatal neurodegenerative disease caused by the degeneration of motor neurons. It is marked by gradual degeneration of the central nervous system nerve cells that control voluntary muscle movement. As motor neurons degenerate, they can no longer send impulses to the muscle fibers that normally result in muscle movement. Early symptoms of ALS often include increasing muscle weakness, especially involving the arms and legs, speech, swallowing or breathing. Riluzole is approved in the US and Europe for treating ALS.
U.S. Pat. No. 5,527,814 discloses the use of riluzole for treating ALS; the riluzole-based formulations exemplified in this patent are a tablet, a hard gelatine capsule and an injectable solution.
U.S. Pat. No. 6,432,992 discloses the use of riluzole for the treatment of adrenoleukodystrophy; also the riluzole-based formulations exemplified in this patent are a tablet, a hard gelatine capsule and an injectable solution.
Oral Riluzole is commercially available as capsule-shaped, white, film-coated tablets containing 50 mg active. Currently there are no commercially available liquid formulations of riluzole.
As opposed to tablets, an oral liquid formulation would increase ALS patients compliance when difficulties in swallowing arise.
Riluzole has a very low solubility in water, about 0.3 mg/mL at neutral pH. Although under acidic conditions the solubility of Riluzole increases and at pH 1.2 is about 12 mg/mL, its chemical stability decreases dramatically. So aqueous acidic solutions for oral use are not feasible.
Nevertheless, it is possible to prepare aqueous solutions having concentrations of riluzole between 0.25 and 10% w/v that are not only technically feasible (for example by using co-solvents or solubilizers to increase riluzole aqueous solubility) but also physically and chemically stable. These solutions, however, exhibit very poor palatability due to a significant and persistent (lasting more than 20-30 minutes) anesthetic effect in the mouth, which is due to the intrinsic property of the drug itself.
Due to its lipophilic character and Its low water solubility, riluzole is a good candidate for a suspension formulation.